U.S. patent number 10,375,825 [Application Number 15/289,453] was granted by the patent office on 2019-08-06 for power module substrate, power module substrate with heat sink, power module, method of manufacturing power module substrate, and copper member-bonding paste.
This patent grant is currently assigned to MITSUBISHI MATERIALS CORPORATION. The grantee listed for this patent is MITSUBISHI MATERIALS CORPORATION. Invention is credited to Yoshirou Kuromitsu, Yoshiyuki Nagatomo, Kimihito Nishikawa, Nobuyuki Terasaki.
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United States Patent |
10,375,825 |
Terasaki , et al. |
August 6, 2019 |
Power module substrate, power module substrate with heat sink,
power module, method of manufacturing power module substrate, and
copper member-bonding paste
Abstract
This power module substrate includes a copper plate that is
formed of copper or a copper alloy and is laminated on a surface of
a ceramic substrate 11; a nitride layer 31 that is formed on the
surface of the ceramic substrate 11 between the copper plate and
the ceramic substrate 11; and an Ag--Cu eutectic structure layer 32
having a thickness of 15 .mu.m or less that is formed between the
nitride layer and the copper plate.
Inventors: |
Terasaki; Nobuyuki (Saitama,
JP), Nagatomo; Yoshiyuki (Saitama, JP),
Nishikawa; Kimihito (Gotenba, JP), Kuromitsu;
Yoshirou (Saitama, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI MATERIALS CORPORATION |
Tokyo |
N/A |
JP |
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Assignee: |
MITSUBISHI MATERIALS
CORPORATION (Tokyo, JP)
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Family
ID: |
51553778 |
Appl.
No.: |
15/289,453 |
Filed: |
October 10, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170034905 A1 |
Feb 2, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14374092 |
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9504144 |
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PCT/JP2013/052347 |
Feb 1, 2013 |
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Foreign Application Priority Data
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Feb 1, 2012 [JP] |
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2012-020171 |
Feb 1, 2012 [JP] |
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2012-020172 |
Dec 6, 2012 [JP] |
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2012-267298 |
Dec 6, 2012 [JP] |
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2012-267299 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C
28/00 (20130101); H05K 13/0465 (20130101); B23K
1/0016 (20130101); C04B 37/026 (20130101); H05K
1/09 (20130101); C22C 27/02 (20130101); G01B
15/02 (20130101); C22C 21/00 (20130101); H05K
1/0271 (20130101); B23K 35/3006 (20130101); C04B
37/025 (20130101); H05K 1/0203 (20130101); H05K
1/18 (20130101); C22C 30/04 (20130101); B23K
1/0008 (20130101); C22C 5/06 (20130101); B23K
35/36 (20130101); C22C 14/00 (20130101); B23K
35/262 (20130101); B23K 35/32 (20130101); H01L
23/3735 (20130101); C22C 27/00 (20130101); C22F
1/08 (20130101); B23K 35/365 (20130101); C04B
35/632 (20130101); B23K 35/025 (20130101); G01N
23/203 (20130101); H05K 1/181 (20130101); H05K
3/388 (20130101); H05K 1/0306 (20130101); B23K
35/30 (20130101); C22C 16/00 (20130101); C04B
2235/44 (20130101); H01L 2924/01322 (20130101); H05K
2201/0175 (20130101); C04B 2237/128 (20130101); C04B
2237/704 (20130101); H01L 2224/32225 (20130101); C04B
2237/08 (20130101); C04B 2237/708 (20130101); C04B
2237/368 (20130101); C04B 2237/706 (20130101); G01N
2223/633 (20130101); C04B 2237/60 (20130101); C04B
2237/121 (20130101); C04B 2237/122 (20130101); C04B
2237/366 (20130101); B23K 2101/42 (20180801); C04B
2237/407 (20130101); C04B 2237/72 (20130101); C04B
2237/127 (20130101); C04B 2237/402 (20130101); Y10T
428/12542 (20150115); C04B 2237/125 (20130101); C04B
2237/126 (20130101); C04B 2237/124 (20130101); H01L
2924/01322 (20130101); H01L 2924/00 (20130101) |
Current International
Class: |
H05K
1/02 (20060101); H05K 1/09 (20060101); H05K
1/18 (20060101); H05K 3/38 (20060101); H05K
13/04 (20060101); B23K 35/02 (20060101); B23K
35/30 (20060101); B23K 35/32 (20060101); C22C
5/06 (20060101); C04B 37/02 (20060101); C04B
35/632 (20060101); B23K 35/26 (20060101); B23K
35/365 (20060101); C22C 30/04 (20060101); G01B
15/02 (20060101); G01N 23/203 (20060101); C22C
14/00 (20060101); C22C 16/00 (20060101); C22C
21/00 (20060101); C22C 27/00 (20060101); C22C
27/02 (20060101); C22C 28/00 (20060101); C22F
1/08 (20060101); H01L 23/373 (20060101); B23K
1/00 (20060101); B23K 35/36 (20060101); H05K
1/03 (20060101) |
Field of
Search: |
;228/121
;428/332,336,469,472,298 |
References Cited
[Referenced By]
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3171234 |
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3211856 |
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Sep 2001 |
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JP |
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2002-274964 |
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Sep 2002 |
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JP |
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2003-055058 |
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JP |
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2003-055059 |
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Feb 2003 |
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JP |
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2003-192462 |
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Jul 2003 |
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JP |
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2003-197824 |
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Jul 2003 |
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JP |
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2003-285195 |
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Oct 2003 |
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JP |
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2005-112677 |
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Apr 2005 |
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JP |
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2005-116602 |
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Apr 2005 |
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JP |
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2005-268821 |
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Sep 2005 |
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JP |
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2006-120973 |
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May 2006 |
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JP |
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2007-035353 |
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Feb 2007 |
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JP |
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2008-034860 |
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Feb 2008 |
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JP |
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2010-114469 |
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May 2010 |
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JP |
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2011-091184 |
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May 2011 |
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1998-080073 |
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Nov 1998 |
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KR |
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10-0371974 |
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Feb 2003 |
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KR |
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WO-98/54761 |
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Dec 1998 |
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WO |
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Other References
Opposition mailed Jul. 12, 2017, issued for the Japanese patent
application No. 2015-127751 and a partial translation thereof.
cited by applicant .
Office Action dated Dec. 21, 2017, issued for the European patent
application No. 13742826.4. cited by applicant .
International Search Report dated Mar. 19, 2013, issued for
PCT/JP2013/052347. cited by applicant .
Office Action dated Nov. 12, 2013, issued for the Japanese patent
application No. 2012-267298 and English translation thereof. cited
by applicant .
Office Action dated Nov. 12, 2013, issued for the Japanese patent
application No. 2012-267299 and English translation thereof. cited
by applicant .
Appeal Decision dated Jun. 30, 2015, issued for the Japanese patent
application No. 2012-267298 and a partial translation thereof.
cited by applicant .
Office Action dated Aug. 25, 2015, issued for the Japanese patent
application No. 2014-143522 and English translation thereof. cited
by applicant .
Search Report dated Jan. 5, 2016, issued for the European patent
application No. 13742826.4. cited by applicant .
Office Action dated Feb. 9, 2016, issued for the Japanese patent
application No. 2015-127751 and English translation thereof. cited
by applicant .
Office Action dated Jan. 22, 2019, issued for the Korean Patent
Application No. 10-2014-7020529 and English machine translation
thereof. cited by applicant.
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Primary Examiner: Turner; Archene A
Attorney, Agent or Firm: Locke Lord LLP
Parent Case Text
This application is a divisional application of U.S. application
Ser. No. 14/374,092 filed Jul. 23, 2014 which is a U.S. National
Stage Entry under 35 U.S.C. .sctn. 371 of PCT/JP2013/052347 filed
on Feb. 1, 2013 and claims the right of priority under 35 U.S.C.
.sctn. 119 based on Japanese Patent Application Nos. 2012-267299
filed Dec. 6, 2012, 2012-267298 filed Dec. 6, 2012, 2012-020172
filed Feb. 1, 2012 and 2012-020171 filed Feb. 1, 2012.
Claims
The invention claimed is:
1. A power module substrate, comprising: a ceramic substrate that
is formed of AlN or Si.sub.3N.sub.4 and has a first surface; a
copper plate that is formed of copper or a copper alloy and is
laminated and bonded on the first surface of the ceramic substrate;
a nitride layer that contains at least one nitride of elements
selected from Ti, Hf, Zr, and Nb, is formed on the first surface of
the ceramic substrate between the copper plate and the ceramic
substrate and the nitride layer contains one or two or more
additional elements selected from In, Al, Mn and Zn; and an Ag--Cu
eutectic structure layer that has a thickness of 15 .mu.m or less
and is formed between the nitride layer and the copper plate,
wherein the thickness of the Ag--Cu eutectic structure layer is
measured by a method comprising: obtaining a backscattered electron
image of an interface between the copper plate and the ceramic
substrate using an EPMA; based on the backscattered electron image,
measuring the area of the Ag--Cu eutectic structure layer
continuously formed on the bonding interface in a measurement
visual field at a magnification of 2000 times; dividing the area of
the Ag--Cu eutectic structure layer by the width of the measurement
visual field, and obtaining the average of the thicknesses in five
measurement visual fields as the thickness of the Ag--Cu eutectic
structure layer.
2. The power module substrate according to claim 1, wherein the
ceramic substrate is formed of AlN, and the thickness of the Ag--Cu
eutectic structure layer is 14 .mu.m or less.
3. The power module substrate according to claim 1, wherein the
ceramic substrate is formed of Si.sub.3N.sub.4, and the thickness
of the Ag--Cu eutectic structure layer is 1 .mu.m or less.
4. A power module substrate according to claim 1, wherein the power
module substrate has no crack after repeating cooling-heating
cycles of -45.degree. C. to 125.degree. C. for 3500 times on the
power module substrate.
5. A power module substrate with a heat sink, comprising: the power
module substrate according to claim 1; and a heat sink that cools
the power module substrate.
6. A power module, comprising: the power module substrate according
to claim 1; and an electronic component that is mounted on the
power module substrate.
7. A power module substrate, comprising: a ceramic substrate that
is formed of AlN or Si3N4 and has a first surface; a copper plate
that is formed of copper or a copper alloy and is laminated and
bonded on the first surface of the ceramic substrate; a nitride
layer that contains a nitride of Nb and is formed on the first
surface of the ceramic substrate between the copper plate and the
ceramic substrate; and an Ag--Cu eutectic structure layer that has
a thickness of 15 .mu.m or less and is formed between the nitride
layer and the copper plate, wherein the thickness of the Ag--Cu
eutectic structure layer is measured by a method comprising:
obtaining a backscattered electron image of an interface between
the copper plate and the ceramic substrate using an EPMA; based on
the backscattered electron image, measuring the area of the Ag--Cu
eutectic structure layer continuously formed on the bonding
interface in a measurement visual field at a magnification of 2000
times; dividing the area of the Ag--Cu eutectic structure layer by
the width of the measurement visual field, and obtaining the
average of the thicknesses in five measurement visual fields as the
thickness of the Ag--Cu eutectic structure layer.
Description
TECHNICAL FIELD
The present invention relates to a power module substrate used in a
semiconductor device for controlling a high current and a high
voltage, a power module substrate with a heat sink, a power module,
a method of manufacturing a power module substrate, and a copper
member-bonding paste.
Priority is claimed on Japanese Patent Application No. 2012-020171,
filed Feb. 1, 2012, Japanese Patent Application No. 2012-020172,
filed Feb. 1, 2012, Japanese Patent Application No. 2012-267298,
filed Dec. 6, 2012, and Japanese Patent Application No.
2012-267299, filed Dec. 6, 2012, the contents of which are
incorporated herein by reference.
BACKGROUND ART
Among semiconductor elements, a power module for supplying power
has a relatively high amount of heat generation. Therefore, as a
substrate on which this power module is mounted, for example, a
power module substrate including: a ceramic substrate that is
formed of AlN (aluminum nitride), Al.sub.2O.sub.3 (alumina), or
Si.sub.3N.sub.4 (silicon nitride); a circuit layer in which a first
metal plate is bonded to one surface of the ceramic substrate; and
a metal layer in which a second metal plate is bonded to the other
surface of the ceramic substrate is used.
In such a power module substrate, a semiconductor element such as a
power element is mounted on the circuit layer through a solder
material.
PTL 1 discloses a power module substrate in which an aluminum plate
is used as the first metal plate (circuit layer) and the second
metal plate (metal layer).
PTLs 2 and 3 disclose a power module substrate in which a copper
plate is used as the first metal plate (circuit layer) and the
second metal plate (metal layer), and the copper plate is bonded to
a ceramic substrate with an active metal method using an
Ag--Cu--Ti-based brazing material.
CITATION LIST
Patent Literature
[PTL 1] Japanese Patent No. 3171234 [PTL 2] Japanese Unexamined
Patent Application, First Publication No. S60-177634 [PTL 3]
Japanese Patent No. 3211856
DISCLOSURE OF INVENTION
Technical Problem
In the power module substrate disclosed in PTL 1, the aluminum
plate is used as the first metal plate forming the circuit layer.
The thermal conductivity of aluminum is lower than that of copper.
Therefore, when the aluminum plate is used as the circuit layer,
heat generated from a heating element of an electrical components
or the like mounted on the circuit layer cannot be spread and
dissipated compared to a case where a copper plate is used.
Therefore, when the power density is increased along with a
decrease in the size and an increase in the power of an electronic
component, there is a concern that heat may not be sufficiently
dissipated.
In PTLs 2 and 3, since the circuit layer is formed using the copper
plate, heat generated from a heating element of an electrical
component or the like mounted on the circuit layer can be
efficiently dissipated. As disclosed in PTLs 2 and 3, when the
copper plate and the ceramic substrate are bonded with the active
metal method, the Ag--Cu--Ti-based brazing material is melted by a
reaction of Cu and Ag and solidified on a bonding portion between
the copper plate and the ceramic substrate. As a result, the copper
member and the ceramic member are bonded to each other, and an
Ag--Cu eutectic structure layer is formed.
The Ag--Cu eutectic structure layer is extremely hard. Therefore,
when a cooling-heating cycle is applied to the above-described
power module substrate, and when a shearing stress is generated by
a difference in thermal expansion coefficient between the ceramic
substrate and the copper plate, there is a problem in that, for
example, the ceramic substrate is cracked without the Ag--Cu
eutectic structure layer being deformed.
The present invention has been made in consideration of the
above-described circumstances, and an object thereof is to provide
a power module substrate in which a copper plate formed of copper
or a copper alloy is bonded to a ceramic substrate, and the
cracking of the ceramic substrate can be suppressed during the
application of a cooling-heating cycle; a power module substrate
with a heat sink; a power module; a method of manufacturing a power
module substrate; and a copper member-bonding paste.
Technical Solution
In order to solve the above-described problems, according to an
aspect of the present invention, a power module substrate is
provided, including: a copper plate that is formed of copper or a
copper alloy and is laminated and bonded on a surface of a ceramic
substrate; a nitride layer that is formed on the surface of the
ceramic substrate between the copper plate and the ceramic
substrate; and an Ag--Cu eutectic structure layer having a
thickness of 15 .mu.m or less that is formed between the nitride
layer and the copper plate.
In this power module substrate, the thickness of the Ag--Cu
eutectic structure layer formed in a bonding portion between the
copper plate and the ceramic substrate is 15 .mu.m or less.
Therefore, even when a shearing stress is generated by a difference
in thermal expansion coefficient between the ceramic substrate and
the copper plate during the application of a cooling-heating cycle,
the copper plate is appropriately deformed, and thus the cracking
of the ceramic substrate can be suppressed. In addition, since the
nitride layer is formed on the surface of the ceramic substrate,
the ceramic substrate and the copper plate can be reliably bonded
to each other.
It is preferable that the ceramic substrate be formed of either AlN
or Si.sub.3N.sub.4. In this case, nitrogen and a nitride-forming
element contained in the ceramic substrate react with each other.
As a result, a nitride layer (which is formed of a nitride
different from a nitride forming the ceramic substrate) is formed
on the surface of the ceramic substrate, and thus the ceramic
substrate and the nitride layer are strongly combined.
It is preferable that the nitride layer contain a nitride of one or
two or more elements (nitride-forming elements) selected from Ti,
Hf, Zr, and Nb. In this case, the ceramic substrate and the nitride
layer are strongly combined, and thus the ceramic substrate and the
copper plate can be strongly combined.
According to another aspect of the invention, a power module
substrate with a heat sink is provided, including: the
above-described power module substrate; and a heat sink that is
bonded to the power module substrate and cools the power module
substrate.
According to the heat sink-equipped power module substrate having
the above-described configuration, heat generated from the power
module substrate can be dissipated by the heat sink. Since the
copper plate and the ceramic substrate are reliably bonded to each
other, heat generated from the power module substrate can be
reliably conducted to the heat sink side.
According to still another aspect of the present invention, a power
module is provided, including: the above-described power module
substrate; and an electronic component that is mounted on the power
module substrate.
According to the power module having the above-described
configuration, heat generated from an electronic component mounted
on a circuit layer can be efficiently dissipated. In addition, even
an increase in the power density (amount of heat generation) of an
electronic component can be sufficiently handled.
According to still another aspect of the present invention, a
method is provided of manufacturing a power module substrate
including a copper plate that is formed of copper or a copper alloy
and is laminated and bonded on a surface of a ceramic substrate,
the method including: a copper member-bonding paste coating process
of forming an Ag-nitride-forming element layer, which contains Ag
and a nitride-forming element, on at least one of a bonding surface
of the ceramic substrate and a bonding surface of the copper plate;
a laminating process of laminating the ceramic substrate and the
copper plate through the Ag-nitride-forming element layer; a
heating process of pressing and heating a laminate of the ceramic
substrate and the copper plate in a laminating direction to form a
molten metal region at an interface between the ceramic substrate
and the copper plate; and a solidification process of solidifying
the molten metal region to bond the ceramic substrate and the
copper plate to each other, in which in the heating process, Ag is
diffused to the copper plate side to form the molten metal region
at the interface between the ceramic substrate and the copper plate
and to form a nitride layer on a surface of the ceramic
substrate.
According to the method of manufacturing a power module substrate
having the above-described configuration, in the heating process,
Ag is diffused to the copper plate side to form the molten metal
region at the interface between the ceramic substrate and the
copper plate. Therefore, the thickness of the molten metal region
can be suppressed to be small, and the thickness of the Ag--Cu
eutectic structure layer formed in the molten metal region can be
suppressed to be 15 .mu.m or less. In the heating process, since a
nitride layer is formed on a surface of the ceramic substrate, the
ceramic substrate and the copper plate can be strongly bonded to
each other. The thickness of the Ag--Cu eutectic structure layer
may be, for example, 0.1 .mu.m to 15 .mu.m.
It is preferable that the nitride-forming element be one or two or
more elements selected from Ti, Hf, Zr, and Nb. In this case, a
nitride layer containing a nitride of Ti, Hf, Zr, or Nb can be
formed on the surface of the ceramic substrate, and the ceramic
substrate and the copper plate can be strongly bonded to each
other. From the viewpoint of cost, Ti is a particularly preferable
element.
It is preferable that, in the copper member-bonding paste coating
process, one or two or more additional elements selected from In,
Sn, Al, Mn, and Zn be added in addition to Ag and the
nitride-forming element. In this case, since the melting point is
decreased in the heating process, the molten metal region can be
formed at a lower temperature, and thus the thickness of the Ag--Cu
eutectic structure layer can be further reduced.
It is preferable that, in the copper member-bonding paste coating
process, a paste containing Ag and a nitride-forming element be
coated. In this case, an Ag-nitride-forming element layer can be
reliably formed on at least one of a bonding surface of the ceramic
substrate and a bonding surface of the copper plate.
The Ag-nitride-forming element layer-containing paste may contain a
hydride of the nitride-forming element. In this case, since
hydrogen of the hydride of the nitride-forming element functions as
a reducing agent, an oxide film and the like formed on the surface
of the copper plate can be removed, and the diffusion of Ag and the
formation of the nitride layer can be reliably performed.
According to still another aspect of the present invention, a
copper member-bonding paste is provided which is used when a copper
member formed of copper or a copper alloy and a ceramic member are
bonded to each other, the copper member-bonding paste including: a
powder component containing Ag and a nitride-forming element; a
resin; and a solvent, in which a composition of the powder
component contains 0.4 mass % to 75 mass % of the nitride-forming
element and a balance consisting of Ag and unavoidable
impurities.
The copper member-bonding paste having the above-described
configuration includes the powder component containing Ag and a
nitride-forming element. Therefore, when the paste is coated on a
bonding portion between the copper member and the ceramic member
and is heated, Ag in the powder component is diffused to the copper
member side such that a molten metal region is formed by a reaction
of Cu and Ag. By the molten metal region being solidified, the
copper member and the ceramic member are bonded to each other.
That is, since the molten metal region is formed by the diffusion
of Ag to the copper member, the molten metal region is not formed
to be thicker than necessary in the bonding portion, and the
thickness of the Ag--Cu eutectic structure layer formed after the
bonding (after the solidification) can be reduced. As such, since
the thickness of the hard Ag--Cu eutectic structure layer is small,
the cracking of the ceramic member can be suppressed.
In addition, since the composition of the powder component contains
0.4 mass % to 75 mass % of the nitride-forming element and a
balance consisting of Ag and unavoidable impurities, a nitride
layer can be formed on the surface of the ceramic member. As such,
since the ceramic member and the copper member are bonded to each
other through the nitride layer, the bonding strength between the
ceramic substrate and the copper plate can be improved.
When the content of the nitride-forming element is less than 0.4
mass %, the nitride layer cannot be reliably formed, and there is a
concern that the bonding strength between the ceramic substrate and
the copper plate may be decreased. When the content of the
nitride-forming element is greater than 75 mass %, the amount of Ag
diffused to the copper member cannot be secured, and there is a
concern that the ceramic substrate and the copper plate may not be
joined to each other. Based on the above points, the content of the
nitride-forming element in the powder component is set in a range
from 0.4 mass % to 75 mass %.
The powder component may be a mixture of Ag powder and powder of
the nitride-forming element or may be powder of an alloy of Ag and
the nitride-forming element.
It is preferable that a particle size of powder forming the powder
component be 40 .mu.m or less. In this case, the copper
member-joining paste can be coated to be thin. Accordingly, the
thickness of the Ag--Cu eutectic structure layer formed after the
bonding (after the solidification) can be further reduced. The
particle size of the powder may be, for example, 0.01 .mu.m to 40
.mu.m.
It is preferable that the content of the powder component be 40
mass % to 90 mass %. In this case, since the content of the powder
component is 40 mass % or greater, the molten metal region can be
reliably formed by diffusing Ag to the copper member, and the
copper member and the ceramic member can be bonded to each other.
The nitride layer can be reliably formed on the surface of the
ceramic member. On the other hand, since the content of the powder
component is 90 mass % or less, the contents of the resin and the
solvent can be secured, and the paste can be reliably coated in the
bonding portion between the copper member and the ceramic
member.
The powder component may contain a hydride of the nitride-forming
element.
In this case, since hydrogen of the hydride of the nitride-forming
element functions as a reducing agent, an oxide film and the like
formed on the surface of the copper plate can be removed, and the
diffusion of Ag and the formation of the nitride layer can be
reliably performed.
Further, it is preferable that the powder component further contain
one or two or more additional elements selected from In, Sn, Al,
Mn, and Zn in addition to Ag and the nitride-forming element; and
that the content of Ag be at least 25 mass % or greater.
In this case, the molten metal region can be formed at a lower
temperature, unnecessary diffusion of Ag can be suppressed, and
thus the thickness of the Ag--Cu eutectic structure layer can be
further reduced.
It is preferable that the powder component further contain a
dispersant in addition to the resin and the solvent. In this case,
the powder component can be easily dispersed, Ag can be uniformly
diffused, and the nitride layer can be uniformly formed.
It is preferable that the powder component further contain a
plasticizer in addition to the resin and the solvent. In this case,
a shape of the copper member-bonding paste can be relatively freely
formed, and the paste can be reliably coated in the bonding portion
between the copper member and the ceramic member.
It is preferable that the powder component further contain a
reducing agent in addition to the resin and the solvent. In this
case, due to the effect of the reducing agent, an oxide film and
the like formed on the surface of the powder component can be
removed, and the diffusion of Ag and the formation of the nitride
layer can be reliably performed.
According to still another aspect of the present invention, a
method of manufacturing a bonded body is provided in which a copper
member formed of copper or a copper alloy and a ceramic member are
bonded to each other, the method including: heating a laminate in
which the copper member-bonding paste is interposed between the
copper member and the ceramic member to bond the copper member and
the ceramic member to each other.
In this case, a molten metal region can be formed by diffusing Ag,
which is contained in the copper member-bonding paste, to the
copper member side, and the copper member and the ceramic member
can be bonded to each other by solidifying the molten metal region.
Accordingly, since the thickness of the hard Ag--Cu eutectic
structure layer is small, the cracking of the ceramic member can be
suppressed.
A nitride layer can be formed on the surface of the ceramic member,
and the bonding strength between the ceramic member and the copper
member can be improved.
Advantageous Effects of Invention
According to the present invention, it is possible to provide a
power module substrate in which a copper plate formed of copper or
a copper alloy is bonded to a ceramic substrate, and the cracking
of the ceramic substrate can be suppressed during the application
of a cooling-heating cycle; a power module substrate with a heat
sink; a power module; and a method of manufacturing a power module
substrate.
In addition, it is possible to provide a copper member-bonding
paste capable of suppressing, even when a copper member and a
ceramic member are bonded to each other, the cracking of the
ceramic member without increasing the thickness of a hard Ag--Cu
eutectic structure layer and capable of reliably bonding the copper
member and the ceramic member to each other; and a method of
manufacturing a bonded body in which the copper member-bonding
paste is used.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a cross-sectional view illustrating a power module
substrate according to a first embodiment of the present invention;
and a power module substrate with a heat sink and a power module in
which the above-described power module substrate is used.
FIG. 2 is a cross-sectional view illustrating a bonding interface
between a circuit layer and a ceramic substrate of FIG. 1.
FIG. 3 is a flowchart illustrating a method of manufacturing a
copper member-bonding paste which is used when a copper plate and a
ceramic substrate are bonded to each other in the first
embodiment.
FIG. 4 is a flowchart illustrating a method of manufacturing the
power module substrate according to the first embodiment and a
method of manufacturing a power module substrate with a heat sink
in which the above-described power module substrate is used.
FIG. 5 is a cross-sectional view illustrating the method of
manufacturing the power module substrate according to the first
embodiment and the method of manufacturing a power module substrate
with a heat sink in which the above-described power module
substrate is used.
FIG. 6 is a cross-sectional view illustrating a process of bonding
a ceramic substrate and a copper plate to each other.
FIG. 7 is a cross-sectional view illustrating a power module
substrate according to a second embodiment of the present
invention.
FIG. 8 is a cross-sectional view illustrating bonding interfaces
between a circuit layer and a ceramic substrate and between a metal
layer and the ceramic substrate in FIG. 7.
FIG. 9 is a flowchart illustrating a method of manufacturing the
power module substrate according to the second embodiment.
FIG. 10 is a cross-sectional view illustrating the method of
manufacturing the power module substrate according to the second
embodiment.
FIG. 11 is a cross-sectional view illustrating a method of
manufacturing a power module substrate according to another
embodiment of the present invention and a method of manufacturing a
power module substrate with a heat sink in which the
above-described power module substrate is used.
FIG. 12 is a cross-sectional view illustrating a method of
manufacturing a power module substrate according to still another
embodiment of the present invention and a method of manufacturing a
power module substrate with a heat sink in which the
above-described power module substrate is used.
FIG. 13 is a cross-sectional view illustrating a method of
manufacturing a power module substrate according to still another
embodiment of the present invention and a method of manufacturing a
power module substrate with a heat sink in which the
above-described power module substrate is used.
FIG. 14 is a plan view illustrating positions where the thickness
is measured in Examples.
DESCRIPTION OF EMBODIMENTS
Hereinafter, a power module substrate, a power module substrate
with a heat sink, and a power module according to embodiments of
the present invention will be described with reference to the
accompanying drawings.
First Embodiment
First, a first embodiment of the present invention will be
described. FIG. 1 illustrates a power module substrate with a heat
sink 50 and a power module 1 in which a power module substrate 10
according to the first embodiment is used.
The power module 1 includes the power module substrate 10 on which
a circuit layer 12 is disposed; a semiconductor element 3
(electronic component) that is bonded to a surface of the circuit
layer 12 through a solder layer 2; a buffer plate 41; and a heat
sink 51. The solder layer 2 is formed of, for example, a
Sn--Ag-based, Sn--In-based, or Sn--Ag--Cu-based solder material. In
the embodiment, a Ni plating layer (not illustrated) is provided
between the circuit layer 12 and the solder layer 2.
The power module substrate 10 includes a ceramic substrate 11; a
circuit layer 12 that is disposed on one surface (upper surface in
FIG. 1) of the ceramic substrate 11; and a metal layer 13 that is
disposed on the other surface (lower surface in FIG. 1) of the
ceramic substrate 11.
The ceramic substrate 11 prevents electric connection between the
circuit layer 12 and the metal layer 13 and is formed of AlN
(aluminum nitride) or Si.sub.3N.sub.4 (silicon nitride) having a
high insulating property. The thickness of the ceramic substrate 11
is not limited but is preferably set to be in a range of 0.2 mm to
1.5 mm (in the embodiment, 0.635 mm).
As illustrated in FIG. 5, the circuit layer 12 is formed by bonding
a copper plate 22 to one surface (upper surface in FIG. 5) of the
ceramic substrate 11. The thickness of the circuit layer 12 is not
limited but is preferably set to be in a range of 0.1 mm to 1.0 mm
(in the embodiment, 0.3 mm). In the circuit layer 12, a circuit
pattern is formed, and one surface (upper surface in FIG. 1) of the
circuit layer 12 is a mounting surface on which the semiconductor
element 3 is mounted.
In the embodiment, the copper plate 22 (circuit layer 12) is formed
of a rolled sheet of oxygen-free copper (OFC) having a purity of
99.99 mass % or higher but may be formed of other copper
alloys.
In order to bond the ceramic substrate 11 and the circuit layer 12
to each other, a copper member-bonding paste (described below)
containing Ag and a nitride-forming element is used.
As illustrated in FIG. 5, the metal layer 13 is formed by bonding
an aluminum plate 23 to the other surface (lower surface in FIG. 5)
of the ceramic substrate 11. The thickness of the metal layer 13 is
not limited but is preferably set to be in a range of 0.6 mm to 6.0
mm (in the embodiment, 0.6 mm).
In the embodiment, the aluminum plate 23 (metal layer 13) is formed
of a rolled sheet of aluminum (so-called 4N aluminum) having a
purity of 99.99 mass % or higher but may be optionally formed of
other aluminum alloys.
The buffer plate 41 absorbs strains generated by a cooling-heating
cycle and, as described in FIG. 1, is formed on the other surface
(lower surface in FIG. 1) of the metal layer 13. The thickness of
the buffer plate 41 is not limited but is preferably set to be in a
range of 0.5 mm to 7.0 mm (in the embodiment, 0.9 mm).
In the embodiment, the buffer plate 41 is formed of a rolled sheet
of aluminum (so-called 4N aluminum) having a purity of 99.99 mass %
or higher but may be optionally formed of other aluminum
alloys.
The heat sink 51 dissipates heat generated from the above-described
power module substrate 10. The heat sink 51 according to the
embodiment is bonded to the power module substrate 10 through the
buffer plate 41.
In the embodiment, the heat sink 51 is formed of aluminum or an
aluminum alloy. Specifically, the heat sink 51 is formed of a
rolled sheet of an A6063 alloy but may be optionally formed of
other aluminum alloys. The thickness of the heat sink 51 is not
limited but is preferably set to be in a range of 1 mm to 10 mm (in
the embodiment, 5 mm).
FIG. 2 is an enlarged view illustrating a bonding interface between
the ceramic substrate 11 and the circuit layer 12. On a surface of
the ceramic substrate 11, a nitride layer 31 that is formed of a
nitride of a nitride-forming element contained in the copper
member-bonding paste is formed.
An Ag--Cu eutectic structure layer 32 is formed so as to be
laminated on the nitride layer 31. The thickness of the Ag--Cu
eutectic structure layer 32 is 15 .mu.m or less. The thickness of
the Ag--Cu eutectic structure layer can be measured from a
backscattered electron image obtained using an EPMA (electron probe
microanalyzer) and, for example, may be 0.1 .mu.m to 15 m.
Next, a method of manufacturing the power module substrate 10
having the above-described configuration and a method of
manufacturing the heat sink-equipped power module substrate 50 will
be described.
As described above, in order to bond the ceramic substrate 11 and
the copper plate 22 which forms the circuit layer 12 to each other,
the copper member-bonding paste containing Ag and the
nitride-forming element is used. First, the copper member-bonding
paste will be described.
The copper member-bonding paste includes a powder component
containing Ag and a nitride-forming element, a resin, a solvent, a
dispersant, a plasticizer, and a reducing agent. The dispersant,
the plasticizer, and the reducing agent are optional
components.
The content of the powder component in the entire copper
member-bonding paste is 40 mass % to 90 mass %.
In the embodiment, the viscosity of the copper member-bonding paste
is adjusted to be preferably 10 Pas to 500 Pas and more preferably
50 Pas to 300 Pas. In this range, the copper member-bonding paste
is easily coated.
It is preferable that the nitride-forming element be one or two or
more elements selected from Ti, Hf, Zr, and Nb. In the embodiment,
Ti is contained as the nitride-forming element.
The composition of the powder component contains 0.4 mass % to 75
mass % of the nitride-forming element and a balance consisting of
Ag and unavoidable impurities. The content of the nitride-forming
element may be 0.2 mass % to 85 mass %. In the embodiment, the
composition of the powder component contains 10 mass % of Ti and a
balance consisting of Ag and unavoidable impurities.
In the embodiment, as the powder component containing Ag and the
nitride-forming element (Ti), an alloy powder of Ag and Ti is used.
The alloy powder is prepared using an atomizing method, and the
particle size thereof can be set to be 40 .mu.m or less, preferably
20 .mu.m or less, and more preferably 10 .mu.m or less by sieving
the prepared alloy powder.
The particle size of the alloy powder can be measured using, for
example, a laser diffraction scattering particle size analyzer.
The resin controls the viscosity of the copper member-bonding
paste. For example, as the resin, ethyl cellulose, methyl
cellulose, polymethyl methacrylate, acrylic resin, or alkyd resin
can be used. The content of the resin in the paste may be, for
example, 0.5 mass % to 25 mass %.
The solvent is a solvent for dissolving the above-described powder
component. For example, as the solvent, methyl cellosolve, ethyl
cellosolve, terpineol, toluene, texanol, or triethyl citrate can be
used. The content of the solvent in the paste may be, for example,
5 mass % to 58 mass %.
The dispersant uniformly disperses the powder component. For
example, as the dispersant, an anionic surfactant or a cationic
surfactant can be used. The content of the dispersant in the paste
may be, for example, 0.01 mass % to 5 mass %.
The plasticizer improves the formability of the copper
member-bonding paste. For example, as the plasticizer, dibutyl
phthalate or dibutyl adipate can be used. The content of the
plasticizer in the paste may be, for example, 0.1 mass % to 20 mass
%.
The reducing agent removes an oxide film or the like that is formed
on a surface of the powder component. For example, rosin or abietic
acid can be used. In the embodiment, abietic acid is used. The
content of the reducing agent in the paste may be, for example, 0.5
mass % to 10 mass %.
The dispersant, the plasticizer, and the reducing agent may be
optionally added. The copper member-bonding paste may be formed
without adding the dispersant, the plasticizer, and the reducing
agent.
A method of manufacturing the copper member-bonding paste will be
described with reference to a flowchart of FIG. 3.
First, as described above, the alloy powder containing Ag and the
nitride-forming element (Ti) is prepared using an atomizing method
and is sieved to obtain an alloy powder having a particle size of
40 .mu.m or less (alloy powder preparing process S01).
The solvent and the resin are mixed with each other to prepare an
organic mixture (organic material mixing process S02).
The alloy powder obtained in the alloy powder preparing process
S01, the organic mixture obtained in the organic material mixing
process S02, and auxiliary additives such as the dispersant, the
plasticizer, and the reducing agent are preliminarily mixed with
each other using a mixer (preliminary mixing process S03).
Next, the preliminary mixture is mixed while being kneaded using a
roll mill including plural rolls (kneading process S04).
The kneaded material obtained in the kneading process S04 is
filtered using a paste filter (filtering process S05).
In this way, the above-described copper member-bonding paste is
prepared.
Next, a method of manufacturing the power module substrate 10
according to the embodiment in which the copper member-bonding
paste is used and a method of manufacturing the heat sink-equipped
power module substrate 50 will be described with reference to FIGS.
4 to 6.
(Copper Member-bonding paste Coating Process S11)
As illustrated in FIG. 5, the above-described copper member-bonding
paste is coated on one surface of the ceramic substrate 11 by, for
example, screen printing, followed by drying. As a result, an
Ag-nitride-forming element layer 24 is formed. The thickness of the
Ag-nitride-forming element layer 24 is not particularly limited,
but the thickness thereof after drying is preferably 20 .mu.m to
300 .mu.m.
(Laminating Process S12)
Next, the copper plate 22 is laminated on one surface of the
ceramic substrate 11. That is, the Ag-nitride-forming element layer
24 is interposed between the ceramic substrate 11 and the copper
plate 22.
(Heating Process S13)
Next, the copper plate 22 and the ceramic substrate 11 are charged
into a vacuum heating furnace and heated while being pressed
(pressure: 1 kgf/cm.sup.2 to 35 kgf/cm.sup.2) in a laminating
direction. As a result, as illustrated in FIG. 6, Ag of the
Ag-nitride-forming element layer 24 is diffused to the copper plate
22. At this time, a part of the copper plate 22 is melted by a
reaction between Cu and Ag, and thus a molten metal region 27 is
formed at an interface between the copper plate 22 and the ceramic
substrate 11.
In the embodiment, it is preferable that the internal pressure of
the vacuum heating furnace be set in a range of 10.sup.-6 Pa to
10.sup.-3 Pa and that the heating temperature be set in a range of
790.degree. C. to 850.degree. C.
(Solidification Process S14)
Next, the molten metal region 27 is cooled and solidified to bond
the ceramic substrate 11 and the copper plate 22 to each other.
After the completion of the solidification process S14, Ag of the
Ag-nitride-forming element layer 24 is sufficiently diffused, and
the Ag-nitride-forming element layer 24 does not remain at the
bonding interface between the ceramic substrate 11 and the copper
plate 22.
(Metal Layer Bonding Process S15)
Next, the aluminum plate 23 which forms the metal layer 13 is
bonded to the other surface of the ceramic substrate 11. In the
embodiment, as illustrated in FIG. 5, the aluminum plate 23 which
forms the metal layer 13 is laminated on the other surface of the
ceramic substrate 11 through a brazing foil 25 having a thickness
of, preferably, 5 .mu.m to 50 .mu.m (in the embodiment, 14 .mu.m).
In the embodiment, the brazing foil 25 is preferably formed of an
Al--Si-based brazing material containing Si, which is a melting
point-lowering element.
Next, the ceramic substrate 11 and the aluminum plate 23 are
charged into a heating furnace and heated while being pressed
(preferably, pressure: 1 kgf/cm.sup.2 to 35 kgf/cm.sup.2) in a
laminating direction. As a result, the brazing foil 25 and a part
of the aluminum plate 23 are melted, and thus a molten metal region
is formed at an interface between the aluminum plate 23 and the
ceramic substrate 11. It is preferable that the heating temperature
be 600.degree. C. to 650.degree. C. and that the heating time be 30
minutes to 180 minutes.
Next, the molten metal region formed at the interface between the
aluminum plate 23 and the ceramic substrate 11 is cooled and
solidified to bond the ceramic substrate 11 and the aluminum plate
23 to each other. In this way, the power module substrate 10
according to the embodiment is manufactured.
(Buffer Plate-Heat Sink Bonding Process S16)
Next, as illustrated in FIG. 5, the buffer plate 41 and the heat
sink 51 are laminated on the other surface (lower surface in FIG.
5) of the metal layer 13 of the power module substrate 10 through
brazing foils 42 and 52, respectively.
In the embodiment, the brazing foils 42 and 52 have a thickness of,
preferably, 5 .mu.m to 50 .mu.m (in the embodiment, 14 .mu.m) and
are formed of an Al--Si-based brazing material containing Si, which
is a melting point-lowering element.
Next, the power module substrate 10, the buffer plate 41, and the
heat sink 51 are charged into a heating furnace and heated while
being pressed (preferably, pressure: 1 kgf/cm.sup.2 to 35
kgf/cm.sup.2) in a laminating direction. As a result, molten metal
regions are formed at an interface between the metal layer 13 and
the buffer plate 41 and at an interface between the buffer plate 41
and the heat sink 51, respectively. It is preferable that the
heating temperature be 550.degree. C. to 610.degree. C. and that
the heating time be 30 minutes to 180 minutes.
Next, the molten metal regions which are formed at the interface
between the metal layer 13 and the buffer plate 41 and at the
interface between the buffer plate 41 and the heat sink 51 are
solidified to bond the power module substrate 10, the buffer plate
41, and the heat sink 51 to each other. As a result, the heat
sink-equipped power module substrate 50 according to the embodiment
is manufactured.
The semiconductor element 3 is placed on a surface of the circuit
layer 12 through a solder material and is soldered thereto in a
reducing furnace. As a result, the power module 1 in which the
semiconductor element 3 is bonded to the circuit layer 12 through
the solder layer 2 is manufactured.
According to the power module substrate 10 according to the
embodiment having the above-described configuration, in a bonding
portion between the circuit layer 12 which is formed of the copper
plate 22 and the ceramic substrate 11, the thickness of the Ag--Cu
eutectic structure layer 32 is 15 .mu.m or less. Therefore, even
when a shearing stress is generated by a difference in thermal
expansion coefficient between the ceramic substrate 11 and the
circuit layer 12 during the application of a cooling-heating cycle,
the circuit layer 12 is appropriately deformed, and thus the
cracking of the ceramic substrate 11 can be suppressed.
In addition, since the nitride layer 31 is formed on the surface of
the ceramic substrate 11, the ceramic substrate 11 and the circuit
layer 12 can be reliably bonded to each other.
In the embodiment, since the ceramic substrate 11 is formed of AlN,
the nitride-forming element contained in the copper member-bonding
paste reacts with the ceramic substrate 11. As a result, the
nitride layer 31 is formed on the surface of the ceramic substrate
11, and thus the ceramic substrate 11 and the nitride layer 31 are
strongly combined.
Further, the nitride layer 31 contains a nitride of one or two or
more elements selected from Ti, Hf, Zr, and Nb. Specifically, in
the embodiment, the nitride layer 31 contains TiN. Therefore, the
ceramic substrate 11 and the nitride layer 31 are strongly
combined, and thus the ceramic substrate 11 and the circuit layer
12 are strongly combined.
In the heat sink-equipped power module substrate 50 and the power
module 1 according to the embodiment, heat generated from the power
module substrate 10 can be dissipated by the heat sink 51. Since
the circuit layer 12 and the ceramic substrate 11 are reliably
bonded to each other, heat which is generated from the
semiconductor element 3 mounted on the mounting surface of the
circuit layer 12 can be reliably conducted to the heat sink 51
side, and an increase in the temperature of the semiconductor
element 3 can be suppressed. Accordingly, even an increase in the
power density (amount of heat generation) of the semiconductor
element 3 can be sufficiently handled.
Further, in the heat sink-equipped power module substrate 50 and
the power module 1, the buffer plate 41 is disposed between the
power module substrate 10 and the heat sink 51. Therefore, strains
generated by a difference in thermal expansion coefficient between
the power module substrate 10 and the heat sink 51 can be absorbed
by the deformation of the buffer plate 41.
In addition, in the heating process S13 of the manufacturing method
according to the embodiment, Ag is diffused to the copper plate 22
side to form the molten metal region 27 at the interface between
the ceramic substrate 11 and the copper plate 22. Therefore, the
thickness of the molten metal region 27 can be suppressed to be
small, and the thickness of the Ag--Cu eutectic structure layer 32
can be suppressed to be 15 .mu.m or less. Further, in the heating
process S13, since the nitride layer 31 is formed on the surface of
the ceramic substrate 11, the ceramic substrate 11 and the copper
plate 22 can be strongly bonded to each other.
In addition, in the embodiment, Ti is contained as the
nitride-forming element. Therefore, the ceramic substrate 11 formed
of AlN and Ti react with each other to form the nitride layer 31.
As a result, the ceramic substrate 11 and the copper plate 22 can
be reliably bonded to each other.
Further, in the embodiment, in the copper member-bonding paste
coating process S11, the copper member-bonding paste containing Ag
and the nitride-forming element is coated. Therefore, the
Ag-nitride-forming element layer 24 can be reliably formed on the
bonding surface of the ceramic substrate 11.
In the copper member-bonding paste used in the embodiment, the
composition of the powder component contains 0.4 mass % to 75 mass
% of the nitride-forming element and a balance consisting of Ag and
unavoidable impurities. Therefore, the nitride layer 31 can be
formed on the surface of the ceramic substrate 11. As such, since
the ceramic substrate 11 and the circuit layer 12 which is formed
of the copper plate 22 are bonded to each other through the nitride
layer 31, the bonding strength between the ceramic substrate 11 and
the circuit layer 12 can be improved.
In the embodiment, the particle size of the powder forming the
powder component, that is, the particle size of the alloy powder
containing Ag and the nitride-forming element (Ti) is 40 .mu.m or
less. Therefore, the copper member-bonding paste can be coated to
be thin. Accordingly, the thickness of the Ag--Cu eutectic
structure layer 32 formed after the bonding (after the
solidification) can be reduced.
Since the content of the powder component is 40 mass % to 90 mass
%, the molten metal region 27 can be reliably formed by diffusing
Ag to the copper plate 22, and the copper plate 22 and the ceramic
substrate 11 can be bonded to each other. In addition, the content
of the solvent can be secured, the copper member-bonding paste can
be reliably coated on the bonding surface of the ceramic substrate
11, and the Ag-nitride-forming element layer 24 can be reliably
formed.
In the embodiment, since the dispersant is optionally contained,
the powder component can be easily dispersed, and Ag can be
uniformly diffused. The nitride layer 31 can be uniformly
formed.
Further, in the embodiment, since the plasticizer is optionally
contained, the shape of the copper member-bonding paste can be
relatively freely formed, and the paste can be reliably coated in
the bonding portion of the ceramic substrate 11.
In the embodiment, since the reducing agent is optionally
contained, due to the effect of the reducing agent, an oxide film
and the like formed on the surface of the powder component can be
removed, and the diffusion of Ag and the formation of the nitride
layer 31 can be reliably performed.
Second Embodiment
Next, a second embodiment of the present invention will be
described. FIG. 7 illustrates a power module substrate 110
according to the embodiment. This power module substrate 110
includes a ceramic substrate 111, a circuit layer 112 that is
disposed on one surface (upper surface in FIG. 7) of the ceramic
substrate 111, and a metal layer 113 that is disposed on the other
surface (lower surface in FIG. 7) of the ceramic substrate 111.
The ceramic substrate 111 prevents electric connection between the
circuit layer 112 and the metal layer 113 and is formed of
Si.sub.3N.sub.4 (silicon nitride) having a high insulating
property. The thickness of the ceramic substrate 111 is preferably
set to be in a range of 0.2 mm to 1.5 mm (in the embodiment, 0.32
mm).
As illustrated in FIG. 10, the circuit layer 112 is formed by
bonding a copper plate 122 to one surface (upper surface in FIG.
10) of the ceramic substrate 111. The thickness of the circuit
layer 112 is preferably set to be in a range of 0.1 mm to 1.0 mm
(in the embodiment, 0.6 mm). In the circuit layer 112, a circuit
pattern is formed, and one surface (upper surface in FIG. 7) of the
circuit layer 112 is a mounting surface on which a semiconductor
element is mounted.
In the embodiment, the copper plate 122 (circuit layer 112) is
formed of a rolled sheet of oxygen-free copper (OFC) having a
purity of, preferably, 99.99 mass % or higher.
As illustrated in FIG. 10, the metal layer 113 is formed by bonding
a copper plate 123 to the other surface (lower surface in FIG. 10)
of the ceramic substrate 111. The thickness of the metal layer 113
is preferably set to be in a range of 0.1 mm to 1.0 mm (in the
embodiment, 0.6 mm).
In the embodiment, the copper plate 123 (metal layer 113) is formed
of a rolled sheet of oxygen-free copper (OFC) having a purity of,
preferably, 99.99 mass % or higher.
In order to bond the ceramic substrate 111 and the circuit layer
112 to each other and to bond the ceramic substrate 111 and the
metal layer 113 to each other, a copper member-bonding paste
(described below) containing Ag and a nitride-forming element is
used.
FIG. 8 is an enlarged view illustrating bonding interfaces between
the ceramic substrate 111 and the circuit layer 112 and between the
ceramic substrate 111 and the metal layer 113. On a surface of the
ceramic substrate 111, a nitride layer 131 that is formed of a
nitride of a nitride-forming element contained in the copper
member-bonding paste is formed.
In the embodiment, an Ag--Cu eutectic structure layer observed in
the first embodiment is not clearly observed.
Next, a method of manufacturing the power module substrate 110
having the above-described configuration will be described. In
order to bond the ceramic substrate 111 and the copper plate 122
which forms the circuit layer 112 to each other, the copper
member-bonding paste containing Ag and the nitride-forming element
is used. First, the copper member-bonding paste will be
described.
The copper member-bonding paste used in the embodiment includes a
powder component containing Ag and a nitride-forming element, a
resin, a solvent, a dispersant, a plasticizer, and a reducing
agent.
The powder component contains one or two or more additional
elements selected from In, Sn, Al, Mn, and Zn in addition to Ag and
the nitride-forming element. In the embodiment, the powder
component contains Sn.
The content of the powder component in the entire copper
member-bonding paste be 40 mass % to 90 mass %.
In the embodiment, the viscosity of the copper member-bonding paste
is adjusted to be preferably 10 Pas to 500 Pas and more preferably
50 Pas to 300 Pas.
It is preferable that the nitride-forming element be one or two or
more elements selected from Ti, Hf, Zr, and Nb. In the embodiment,
Zr is contained as the nitride-forming element.
In the composition of the powder component, the content of the
nitride-forming element (in the embodiment, Zr) is 0.4 mass % to 75
mass %, the content of one or two or more additional elements (in
the embodiment, Sn) selected from In, Sn, Al, Mn, and Zn is 0 mass
% to 50 mass %, and a balance consists of Ag and unavoidable
impurities. In this case, the content of Ag is 25 mass % or
greater. In the embodiment, the composition of the powder component
contains 40 mass % of Zr, 20 mass % of Sn, and a balance consisting
of Ag and unavoidable impurities.
In the embodiment, as the powder element, element powders (Ag
powder, Zr powder, Sn powder) are used. The Ag powder, the Zr
powder, and the Sn powder are mixed with each other such that the
entire powder component has the above-described composition.
The particle size of each of the Ag powder, the Zr powder, and the
Sn powder is set to be 40 .mu.m or less, preferably 20 .mu.m or
less, and more preferably 10 .mu.m or less. The particle size of
each of the Ag powder, the Zr powder, and the Sn powder can be
measured using, for example, a laser diffraction scattering
particle size analyzer.
As the resin and the solvent, the same materials as those of the
first embodiment are used. In the embodiment, the dispersant, the
plasticizer, and the reducing agent are optionally added.
The copper member-bonding paste used in the embodiment is
manufactured according to the manufacturing method described in the
first embodiment. That is, the copper member-bonding paste is
manufactured in the same procedure as that of the first embodiment,
except that the Ag powder, the Zr powder, and the Sn powder are
used instead of the alloy powder.
Next, a method of manufacturing the power module substrate 110
according to the embodiment in which the copper member-bonding
paste is used will be described with reference to FIGS. 9 and
10.
(Copper Member-bonding paste Coating Process S111)
First, as illustrated in FIG. 10, the copper member-bonding paste
according to the above-described embodiment is coated on one
surface and the other surface of the ceramic substrate 111 by, for
example, screen printing. As a result, Ag-nitride-forming element
layers 124 and 125 are formed. The thickness of each of the
Ag-nitride-forming element layers 124 and 125 after drying is
preferably 20 .mu.m to 300 .mu.m.
(Laminating Process S112)
Next, the copper plate 122 is laminated on one surface of the
ceramic substrate 111. The copper plate 123 is laminated on the
other surface of the ceramic substrate 111. That is, the
Ag-nitride-forming element layers 124 and 125 are interposed
between the ceramic substrate 111 and the copper plate 122 and
between the ceramic substrate 111 and the copper plate 123,
respectively.
(Heating Process S113)
Next, the copper plate 122, the ceramic substrate 111, and the
copper plate 123 are charged into a vacuum heating furnace and
heated while being pressed (preferably, pressure: 1 kgf/cm.sup.2 to
35 kgf/cm.sup.2) in a laminating direction. As a result, Ag of the
Ag-nitride-forming element layer 124 is diffused to the copper
plate 122, and Ag of the Ag-nitride-forming element layer 125 is
diffused to the copper plate 123.
At this time, Cu and Ag of the copper plate 122 are melted by a
reaction, and thus a molten metal region is formed at an interface
between the copper plate 122 and the ceramic substrate 111. Cu and
Ag of the copper plate 123 are melted by a reaction, and thus a
molten metal region is formed at an interface between the copper
plate 123 and the ceramic substrate 111.
In the embodiment, it is preferable that the internal pressure of
the vacuum heating furnace be set in a range of 10.sup.-6 Pa to
10.sup.-3 Pa and that the heating temperature be set in a range of
790.degree. C. to 850.degree. C.
(Solidification Process S114)
Next, the molten metal regions are solidified to bond the ceramic
substrate 111 and the copper plates 122 and 123 to each other.
After the completion of the solidification process S114, Ag of the
Ag-nitride-forming element layers 124 and 125 is sufficiently
diffused, and the Ag-nitride-forming element layers 124 and 125 do
not remain at the bonding interfaces between the ceramic substrate
111 and the copper plates 122 and 123.
As such, the power module substrate 110 according to the embodiment
is manufactured. In the power module substrate 110, a semiconductor
element is mounted on the circuit layer 112, and a heat sink is
disposed on the other surface of the metal layer 113.
According to the power module substrate 110 according to the
embodiment having the above-described configuration, in a bonding
portion between the circuit layer 112 which is formed of the copper
plate 122 and the ceramic substrate 111, the thickness of each of
the Ag--Cu eutectic structure layers is 15 .mu.m or less. In the
embodiment, the Ag--Cu eutectic structure layers are not clearly
observed. Therefore, even when a shearing stress is generated by a
difference in thermal expansion coefficient between the ceramic
substrate 111 and the circuit layer 112 during the application of a
cooling-heating cycle, the circuit layer 112 is appropriately
deformed, and thus the cracking of the ceramic substrate 111 can be
suppressed. In addition, since the nitride layer 131 is formed on
the surface of the ceramic substrate 111, the ceramic substrate 111
and the circuit layer 112 can be reliably bonded to each other.
In addition, since the molten metal regions are formed by the
diffusion of Ag to the copper plates 122 and 123, the molten metal
regions are not formed to be thicker than necessary in the bonding
portions between the ceramic substrate 111 and the copper plates
122 and 123, and the thickness of each of the Ag--Cu eutectic
structure layers formed after the bonding (after the
solidification) can be reduced. Accordingly, the cracking of the
ceramic substrate 111 can be suppressed.
In addition, in the embodiment, Zr is contained as the
nitride-forming element. Therefore, the ceramic substrate 111
formed of Si.sub.3N.sub.4 and Zr react with each other to form the
nitride layer 131. As a result, the ceramic substrate 111 and the
copper plates 122 and 123 can be reliably bonded to each other.
In the embodiment, as the powder component, one or two or more
additional elements (in the embodiment, Sn) selected from In, Sn,
Al, Mn, and Zn are contained in addition to Ag and the
nitride-forming element (in the embodiment, Zr). Therefore, the
molten metal regions can be formed at a lower temperature, and thus
the thickness of each of the formed Ag--Cu eutectic structure
layers can be further reduced.
According to the method of manufacturing the copper member-bonding
paste according to the embodiment and the method of manufacturing a
bonded body which have the above-described configuration, Ag can be
interposed at the interface between the ceramic substrate 111 and
the copper plate 122 and at the interface between the ceramic
substrate 111 and the copper plate 123. By diffusing Ag to the
copper plates 122 and 123, the molten metal regions can be formed
by a reaction between Cu and Ag. By solidifying the molten metal
regions, the ceramic substrate 111 and the copper plates 122 and
123 can be bonded to each other.
Hereinabove, the embodiments of the present invention have been
described. However, the present invention is not limited thereto,
and various appropriate modifications can be made within a range
not departing from the technical ideas of the present
invention.
For example, in the above description, Ti or Zr is used as the
nitride-forming element. However, the nitride-forming element is
not limited to Ti or Zr, and other nitride-forming elements such as
Hf or Nb may also be used.
The powder component contained in the Ag-nitride-forming element
layer-containing paste (copper member-bonding paste) may contain a
hydride of the nitride-forming element such as TiH.sub.2 or
ZrH.sub.2. In this case, since hydrogen of the hydride of the
nitride-forming element functions as a reducing agent, an oxide
film and the like formed on the surface of the copper plate can be
removed, and the diffusion of Ag and the formation of the nitride
layer can be reliably performed.
In the description of the second embodiment, Sn is added as the
additional element. However, the additional element is not limited
to Sn, and one or two or more additional elements selected from In,
Sn, Al, Mn, and Zn may also be used.
In the above description, the particle size of the powder forming
the powder component is 40 .mu.m or less. However, the particle
size is not particularly limited to 40 .mu.m or less.
In the above description, the dispersant, the plasticizer, and the
reducing agent are contained. However, the present invention is not
limited to this configuration, and the above components may not be
contained. The dispersant, the plasticizer, and the reducing agent
are optionally added.
Further, in the above description, the aluminum plate and the
ceramic substrate or the aluminum plates are bonded to each other
by brazing. However, the bonding method is not limited to brazing,
and casting, metal pasting, or the like may also be used. An
aluminum plate and a ceramic substrate, an aluminum plate and a top
plate, or other aluminum materials may be bonded to each other
using transient liquid phase bonding by disposing Cu, Si, Zn, Ge,
Ag, Mg, Ca, Ga, or Li therebetween.
The present invention is not limited to the power module substrate
and the heat sink-equipped power module substrate which are
manufactured using the manufacturing methods of FIGS. 5, 6, and 10.
A power module substrate and the like which are manufactured using
other manufacturing methods may also be used.
For example, as illustrated in FIG. 11, a configuration may also be
adopted in which a copper plate 222 which forms a circuit layer 212
is bonded to one surface of a ceramic substrate 211 through an
Ag-nitride-forming element layer 224, an aluminum plate 223 which
forms a metal layer 213 is bonded to the other surface of the
ceramic substrate 211 through a brazing foil 225, and a heat sink
251 is bonded to the other surface of the aluminum plate 223
through a brazing foil 252. As such, a power module substrate with
a heat sink 250 including a power module substrate 210 and a heat
sink 251 is manufactured.
As illustrated in FIG. 12, a power module substrate 310 may be
manufactured by bonding a copper plate 322 which forms a circuit
layer 312 to one surface of a ceramic substrate 311 through an
Ag-nitride-forming element layer 324 and bonding an aluminum plate
323 which forms a metal layer 313 to the other surface of the
ceramic substrate 311 through a brazing foil 325. Next, a heat sink
351 may be bonded to the other surface of the metal layer 313
through a brazing foil 352. As such, a power module substrate with
a heat sink 350 including a power module substrate 310 and a heat
sink 351 is manufactured.
Further, as illustrated in FIG. 13, a configuration may also be
adopted in which a copper plate 422 which forms a circuit layer 412
is bonded to one surface of a ceramic substrate 411 through an
Ag-nitride-forming element layer 424, an aluminum plate 423 which
forms a metal layer 413 is bonded to the other surface of the
ceramic substrate 411 through a brazing foil 425, a buffer plate
441 is bonded to the other surface of the aluminum plate 423
through a brazing foil 442, and a heat sink 451 is bonded to the
other surface of the buffer plate 441 through a brazing foil 452.
As such, a power module substrate with a heat sink 450 including a
power module substrate 410, the buffer plate 441, and the heat sink
451 is manufactured.
In the above description, the copper member-bonding paste according
to the embodiment is used when the ceramic substrate and the copper
plate are bonded to each other. However, the present invention is
not limited to this configuration, and the copper member-bonding
paste according to the invention may be used when a ceramic member
and a copper member are bonded to each other.
EXAMPLES
A comparative test which was performed to confirm the effectiveness
of the present invention will be described. Various pastes were
prepared under conditions shown in Tables 1, 2, and 3. In Table 1,
an alloy powder was used as the powder component. In Table 2,
powders (element powders) of the respective elements were used as
the powder component. In Table 3, powders (element powders) of the
respective elements were used as the powder component, and powder
of a hydride of the nitride-forming element was used as the
nitride-forming element. Table 3 shows the content of the
nitride-forming element (content of active metal) as well as a
mixing ratio of the element powder of the hydride of the
nitride-forming element.
An anionic surfactant was used as a dispersant, dibutyl adipate was
used as a plasticizer, and abietic acid was used as a reducing
agent.
A mixing ratio of the resin, the solvent, the dispersant, the
plasticizer, and the reducing agent aside from the powder component
is 7:70:3:5:15 (resin:solvent:dispersant:plasticizer:reducing
agent) by mass ratio.
TABLE-US-00001 TABLE 1 Maximum Ratio of Particle Size Powder Alloy
Powder Mixing Ratio/wt % in Alloy Component Ag Cu Ti Zr Hf Nb In Sn
Mn Al Zn Powder/.mu.m in Paste Example 1 25 75 <5 80% According
2 50 50 <20 40% to 3 90 10 <5 80% Present 4 50 10 40 <10
80% Invention 5 70 10 20 <10 80% 6 88 2 10 <15 70% 7 30 20 50
<20 50% 8 60 20 20 <20 50% 9 99.6 0.4 <5 90% 10 30 50 20
<10 80% 11 50 30 20 <20 40% 12 60 20 20 <15 50% 13 30 70
<5 90% 14 45 50 5 <15 40% 15 50 40 10 <15 60% 16 74.5 0.5
25 <10 80% 17 30 70 <15 70% 18 45 40 15 <10 60% 19 60 30
10 <15 60% 20 60 10 30 <20 70% 21 80 20 <40 60% 22 90 10
<40 60% 23 80 10 10 <30 60% 24 70 30 <30 60% 25 70 30
<40 60% Comparative 1 90 10 <5 80% Example 2 90 10 <5 80%
3 20 80 <30 80% 4 99.8 0.2 <15 80% Conventional 1 70.5 27 2.5
<15 70% Example
TABLE-US-00002 TABLE 2 Maximum Particle Size Ratio of in All Powder
Element Powder Mixing Ratio/wt % Element Component Ag Cu Ti Zr Hf
Nb In Sn Mn Al Zn Powders/.mu.m in Paste Example 51 40 60 <5 40%
According 52 60 40 <15 40% to 53 80 20 <5 80% Present 54 50
30 20 <5 50% Invention 55 40 30 30 <10 40% 56 94 1 5 <15
70% 57 30 40 30 <10 50% 58 50 30 20 <20 60% 59 50 50 <5
70% 60 40 40 20 <10 70% 61 30 30 40 <20 70% 62 60 20 20
<15 90% 63 30 70 <20 40% 64 50 40 10 <5 40% 65 70 20 10
<20 50% 66 89.5 0.5 10 <10 50% 67 30 70 <10 60% 68 35 50
15 <5 40% 69 45 5 50 <15 90% 70 72 3 25 <20 40% 71 80 20
<30 70% 72 70 30 <30 70% 73 70 10 20 <40 80% 74 70 20 10
<40 60% 75 70 20 10 <40 60% Comparative 51 80 20 <5 80%
Example 52 59.8 0.2 40 <15 70% 53 10 80 10 <15 70%
Conventional 51 69 29 2 <15 70% Example
TABLE-US-00003 TABLE 3 Maximum Content of Particle Size Ratio of
Active in All Powder Element Powder Mixing Ratio/wt % Metal/wt %
Element Component Ag TiH.sub.2 ZrH.sub.2 In Sn Mn Al Zn Ti Zr
Powders/.mu.m in Paste Example 81 65 25 10 24.0 <15 60%
According 82 70 10 20 9.6 <40 80% to 83 75 15 10 14.4 <10 70%
Present 84 80 5 15 4.8 <30 80% Invention 85 90 10 9.6 <5 80%
86 80 10 10 9.8 <40 90% 87 65 25 10 24.6 <5 60% 88 75 15 10
14.8 <15 80% 89 75 20 5 19.7 <30 70% 90 95 5 4.9 <10 60%
91 60 30 10 28.8 <15 60% 92 65 20 15 19.2 <20 70% 93 85 10 5
9.6 <40 80% 94 70 5 25 4.8 <5 50% 95 95 5 4.8 <10 50% 96
70 10 20 9.8 <15 70% 97 65 30 5 29.5 <30 70% 98 85 5 10 4.9
<5 60% 99 65 20 15 19.7 <20 40% 100 80 20 19.7 <10 60%
By bonding ceramic substrates and copper plates to each other using
the various pastes shown in Tables 1, 2, and 3, power module
substrates which were manufactured using the structure and the
manufacturing method of FIG. 10, heat sink-equipped power module
substrates which were manufactured using the structure and the
manufacturing method of FIGS. 11 and 12, and heat sink-equipped
power module substrates which were manufactured using the structure
and the manufacturing method of FIGS. 5 and 13 were prepared.
In the power module substrates of FIG. 10, the copper plates were
bonded to one surface and the other surface of the ceramic
substrate using the above-described various pastes, and a circuit
layer and a metal layer were formed of the copper plates. As the
copper plates, a rolled sheet of oxygen-free copper was used.
In the heat sink-equipped power module substrates of FIGS. 11 and
12, the copper plate was bonded to one surface of the ceramic
substrate using the above-described various pastes to form a
circuit layer.
An aluminum plate was bonded to the other surface of the ceramic
substrate through a brazing material to form a metal layer. 4N
aluminum having a purity of 99.99 mass % was used for the aluminum
plate, and a brazing foil consisting of Al-7.5 mass % Si and having
a thickness of 20 .mu.m was used as the brazing material.
Further, the aluminum plate formed of A6063 as a heat sink was
bonded to the other surface of the metal layer through a brazing
material on the metal layer side of the power module substrate. A
brazing foil consisting of Al-7.5 mass % Si and having a thickness
of 70 .mu.m was used as the brazing material.
In the heat sink-equipped power module substrates of FIGS. 5 and
13, the copper plate was bonded to one surface of the ceramic
substrate using the above-described various pastes to form a
circuit layer.
An aluminum plate was bonded to the other surface of the ceramic
substrate through a brazing material to form a metal layer. 4N
aluminum having a purity of 99.99 mass % was used for the aluminum
plate, and a brazing foil consisting of Al-7.5 mass % Si and having
a thickness of 14 .mu.m was used as the brazing material.
Further, the aluminum plate formed of 4N aluminum as a buffer plate
was bonded to the other surface of the metal layer through a
brazing material. A brazing foil consisting of Al-7.5 mass % Si and
having a thickness of 100 .mu.m was used as the brazing
material.
Further, the aluminum plate formed of A6063 as a heat sink was
bonded to the other surface of the buffer plate through a brazing
material on the metal layer side of the power module substrate. A
brazing foil consisting of Al-7.5 mass % Si and having a thickness
of 100 .mu.m was used as the brazing material.
The ceramic substrates and the copper plates were bonded to each
other under conditions shown in Tables 4, 5, and 6.
During brazing between the ceramic substrate and the aluminum
plate, bonding conditions were a vacuum atmosphere, a pressure of
12 kgf/cm.sup.2, a heating temperature of 650.degree. C., and a
heating time of 30 minutes. Further, during brazing between the
aluminum plates, bonding conditions were a vacuum atmosphere, a
pressure of 6 kgf/cm.sup.2, a heating temperature of 610.degree.
C., and a heating time of 30 minutes.
The materials and the sizes of the ceramic substrates are shown in
Tables 4, 5, and 6. The sizes of the copper plates were 37
mm.times.37 mm.times.0.3 mm. The sizes of the aluminum plates
forming the metal layers were 37 mm.times.37 mm.times.2.1 mm in the
case of the heat sink-equipped power module substrates and were 37
mm.times.37 mm.times.0.6 mm in the case of the power module
substrates equipped with the heat sink and the buffer plate. The
sizes of the aluminum plates forming the heat sinks were 50
mm.times.60 mm.times.5 mm. The sizes of the aluminum plates forming
the buffer plates were 40 mm.times.40 mm.times.0.9 mm.
Tables 4, 5, and 6 show the structures and the manufacturing
methods of the power module substrates which were manufactured
using the above-described various pastes, the heat sink-equipped
power module substrates, and the power module substrates equipped
with the heat sink and the buffer plate. Structure "DBC" represents
the power module substrate of FIG. 10. Structure "H-1" represents
the heat sink-equipped power module substrate of FIG. 11. Structure
"H-2" represents the heat sink-equipped power module substrate of
FIG. 12. Structure "B-1" represents the heat sink-equipped power
module substrate of FIG. 13. Structure "B-2" represents the heat
sink-equipped power module substrate of FIG. 5.
TABLE-US-00004 TABLE 4 Bonding Conditions Bonding Ceramic Substrate
Temperature/.degree. C. Load/kgf/cm.sup.2 Material Size Structure
Example 1 820 12 Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32
mm DBC to 2 850 18 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC
According 3 850 18 Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32
mm H-1 Present 4 820 18 AlN 40 mm .times. 40 mm .times. 0.635 mm
H-2 Invention 5 850 18 Si.sub.3N.sub.4 40 mm .times. 40 mm .times.
0.32 mm H-1 6 790 6 Si.sub.3N.sub.4 40 mm .times. 40 mm .times.
0.32 mm B-2 7 850 6 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC 8
820 6 Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm B-1 9 850
12 AlN 40 mm .times. 40 mm .times. 0.635 mm B-1 10 820 18
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm DBC 11 820 12
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm H-2 12 790 12
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm DBC 13 790 6
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm B-1 14 850 12
AlN 40 mm .times. 40 mm .times. 0.635 mm B-2 15 790 18
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm B-2 16 790 18
AlN 40 mm .times. 40 mm .times. 0.635 mm B-1 17 820 12 AlN 40 mm
.times. 40 mm .times. 0.635 mm H-2 18 820 18 AlN 40 mm .times. 40
mm .times. 0.635 mm H-2 19 850 18 AlN 40 mm .times. 40 mm .times.
0.635 mm B-2 20 790 12 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC
21 820 12 Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm DBC
22 850 18 AlN 40 mm .times. 40 mm .times. 0.635 mm H-1 23 850 18
AlN 40 mm .times. 40 mm .times. 0.635 mm H-1 24 820 6 AlN 40 mm
.times. 40 mm .times. 0.635 mm H-2 25 820 6 AlN 40 mm .times. 40 mm
.times. 0.635 mm H-2 Comparative 1 790 18 AlN 40 mm .times. 40 mm
.times. 0.635 mm B-1 Example 2 820 6 AlN 40 mm .times. 40 mm
.times. 0.635 mm B-1 3 790 18 Si.sub.3N.sub.4 40 mm .times. 40 mm
.times. 0.32 mm DBC 4 820 6 AlN 40 mm .times. 40 mm .times. 0.635
mm H-1 Conventional 1 850 12 AlN 40 mm .times. 40 mm .times. 0.635
mm B-1 Example
TABLE-US-00005 TABLE 5 Bonding Conditions Bonding Ceramic Substrate
Temperature/.degree. C. Load/kgf/cm.sup.2 Material Size Structure
Example 51 850 12 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC
According 52 820 6 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC to
53 790 18 Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm B-2
Present 54 790 6 Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32
mm DBC Invention 55 850 3 AlN 40 mm .times. 40 mm .times. 0.635 mm
DBC 56 820 18 AlN 40 mm .times. 40 mm .times. 0.635 mm H-1 57 850 6
AlN 40 mm .times. 40 mm .times. 0.635 mm B-2 58 820 18
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm H-1 59 790 12
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm DBC 60 820 6
AlN 40 mm .times. 40 mm .times. 0.635 mm H-1 61 790 12
Si.sub.3N.sub.4 40 mm .times. 40 mm .times. 0.32 mm H-2 62 850 18
AlN 40 mm .times. 40 mm .times. 0.635 mm B-1 63 820 6 AlN 40 mm
.times. 40 mm .times. 0.635 mm B-1 64 850 6 Si.sub.3N.sub.4 40 mm
.times. 40 mm .times. 0.32 mm B-1 65 850 18 AlN 40 mm .times. 40 mm
.times. 0.635 mm H-1 66 820 18 Si.sub.3N.sub.4 40 mm .times. 40 mm
.times. 0.32 mm DBC 67 790 12 Si.sub.3N.sub.4 40 mm .times. 40 mm
.times. 0.32 mm B-2 68 790 18 Si.sub.3N.sub.4 40 mm .times. 40 mm
.times. 0.32 mm H-1 69 790 12 Si.sub.3N.sub.4 40 mm .times. 40 mm
.times. 0.32 mm B-1 70 850 18 Si.sub.3N.sub.4 40 mm .times. 40 mm
.times. 0.32 mm H-2 71 820 12 AlN 40 mm .times. 40 mm .times. 0.635
mm B-1 72 850 12 AlN 40 mm .times. 40 mm .times. 0.635 mm B-1 73
850 12 AlN 40 mm .times. 40 mm .times. 0.635 mm B-1 74 820 6 AlN 40
mm .times. 40 mm .times. 0.635 mm H-1 75 820 6 AlN 40 mm .times. 40
mm .times. 0.635 mm H-1 Comparative 51 850 12 AlN 40 mm .times. 40
mm .times. 0.635 mm H-2 Example 52 790 18 AlN 40 mm .times. 40 mm
.times. 0.635 mm DBC 53 790 18 AlN 40 mm .times. 40 mm .times.
0.635 mm H-2 Conventional 51 850 12 AlN 40 mm .times. 40 mm .times.
0.635 mm B-1 Example
TABLE-US-00006 TABLE 6 Bonding Conditions Bonding Ceramic Substrate
Temperature/.degree. C. Load/kgf/cm.sup.2 Material Size Structure
Example 81 850 6 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC
According 82 820 3 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC to
83 790 6 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC Present 84
790 18 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC Invention 85
850 12 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC 86 790 12 AlN
40 mm .times. 40 mm .times. 0.635 mm DBC 87 820 6 AlN 40 mm .times.
40 mm .times. 0.635 mm DBC 88 790 6 AlN 40 mm .times. 40 mm .times.
0.635 mm DBC 89 850 3 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC
90 820 12 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC 91 790 12
AlN 40 mm .times. 40 mm .times. 0.635 mm DBC 92 820 6 AlN 40 mm
.times. 40 mm .times. 0.635 mm DBC 93 850 18 AlN 40 mm .times. 40
mm .times. 0.635 mm DBC 94 790 6 AlN 40 mm .times. 40 mm .times.
0.635 mm DBC 95 820 3 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC
96 790 18 AlN 40 mm .times. 40 mm .times. 0.635 mm DBC 97 850 6 AlN
40 mm .times. 40 mm .times. 0.635 mm DBC 98 820 18 AlN 40 mm
.times. 40 mm .times. 0.635 mm DBC 99 790 12 AlN 40 mm .times. 40
mm .times. 0.635 mm DBC 100 850 6 AlN 40 mm .times. 40 mm .times.
0.635 mm DBC
The equivalent thicknesses (average equivalent thicknesses) were
measured as follows, and the measurement results are shown in
Tables 7, 8, and 9.
First, the various pastes shown in Tables 1, 2, and 3 were coated
on surfaces of the ceramic substrates and the copper plates,
followed by drying. The equivalent thicknesses (average equivalent
thicknesses) of the respective elements of the dried various pastes
were measured.
The thicknesses of the coated various pastes were measured three
times using an X-ray fluorescent analysis thickness meter (trade
name "STF 9400" manufactured by SII Nanotechnology Inc.) at
positions (9 positions) shown in FIG. 14, and the average value
thereof was obtained. The thicknesses of known samples were
measured in advance to obtain a relationship between a fluorescent
X-ray intensity and a density. Based on the results, the equivalent
thicknesses of the respective elements were determined from the
fluorescent X-ray intensities measured in the respective
samples.
TABLE-US-00007 TABLE 7 Average Equivalent Thickness/.mu.m Ag Cu Ti
Zr Hf Nb In Sn Mn Al Zn Total Example 1 1.70 4.85 6.55 According 2
5.12 4.87 9.99 to 3 9.94 1.05 10.99 Present 4 2.65 0.51 6.00 9.16
Invention 5 5.69 0.77 4.79 11.25 6 4.94 0.11 2.69 7.74 7 1.19 0.76
9.17 11.12 8 2.12 0.67 5.75 8.54 9 9.43 0.04 9.47 10 1.56 2.48 2.83
6.87 11 1.23 0.70 6.14 8.07 12 2.14 0.68 6.42 9.24 13 1.55 3.44
4.99 14 1.13 1.20 2.13 4.46 15 1.32 1.00 2.03 4.35 16 4.45 0.04
3.55 8.04 17 1.11 2.47 3.58 18 1.73 1.47 3.81 7.01 19 2.25 1.07
2.16 5.48 20 1.41 0.22 3.13 4.76 21 13.51 3.22 16.73 22 14.32 1.52
15.84 23 14.50 2.50 0.58 17.58 24 15.07 6.15 21.22 25 13.99 5.71
19.70 Comparative 1 18.79 0.85 19.64 Example 2 27.14 1.23 28.37 3
22.31 85.05 107.36 4 5.98 0.01 5.99 Conventional 1 16.57 6.05 0.56
23.18 Example
TABLE-US-00008 TABLE 8 Average Equivalent Thickness/.mu.m Ag Cu Ti
Zr Hf Nb In Sn Mn Al Zn Total Example 51 3.35 4.78 8.13 According
52 6.91 4.39 11.30 to 53 8.55 2.04 10.59 Present 54 2.19 1.25 6.62
10.06 Invention 55 1.97 1.40 7.76 11.13 56 10.61 0.11 2.77 13.49 57
1.46 1.86 7.46 10.78 58 1.23 0.70 2.63 4.56 59 4.50 4.29 8.79 60
3.02 2.87 0.48 6.37 61 1.84 1.75 6.80 10.39 62 2.18 0.69 1.16 4.03
63 1.33 2.95 4.28 64 1.25 0.96 4.07 6.28 65 1.27 0.35 1.93 3.55 66
4.86 0.03 5.50 10.39 67 1.54 3.43 4.97 68 1.30 1.77 7.54 10.61 69
1.96 0.21 3.93 6.10 70 1.34 0.05 6.46 7.85 71 15.18 3.62 18.80 72
13.94 5.69 19.63 73 14.78 2.91 1.34 19.03 74 14.92 4.06 0.68 19.66
75 14.93 4.06 0.68 19.67 Comparative 51 23.34 2.39 25.73 Example 52
6.88 0.02 4.39 11.29 53 1.14 8.72 1.10 10.96 Conventional 51 16.23
6.50 0.45 23.18 Example
TABLE-US-00009 TABLE 9 Average Equivalent Thickness/.mu.m Ag Ti Zr
In Sn Mn Al Zn Total Example 81 1.55 0.51 0.26 2.32 According 82
6.20 0.85 1.77 8.82 to 83 8.98 1.69 1.18 11.85 Present 84 6.81 0.43
1.27 8.51 Invention 85 8.25 0.87 9.12 86 7.25 0.88 0.89 9.02 87
2.21 0.83 0.35 3.39 88 10.22 2.01 1.26 13.49 89 2.76 0.71 0.18 3.65
90 8.25 0.44 8.69 91 1.94 0.94 0.33 3.21 92 3.76 1.09 0.87 5.72 93
14.77 1.65 0.86 17.28 94 1.62 0.13 0.62 2.37 95 4.73 0.26 4.99 96
3.63 0.55 1.13 5.31 97 3.89 1.72 0.30 5.91 98 5.65 0.31 0.65 6.61
99 2.40 0.72 0.58 3.70 100 3.10 0.74 3.84
Regarding the power module substrates and the heat sink-equipped
power module substrates obtained as above, the ceramic cracking,
the bonding ratio after the application of a cooling-heating cycle,
whether or not there is a nitride layer, and the thickness of an
Ag--Cu eutectic structure layer were evaluated. The evaluation
results are shown in Tables 10, 11, and 12.
Whether or not there were cracks was determined for each
cooling-heating cycle (-45.degree. C.125.degree. C.) which was
repeated 5000 times. Based on the number of cooling-heating cycles
where cracks were confirmed, the ceramic cracking was
evaluated.
The bonding ratio after the application of a cooling-heating cycle
was calculated according to the following expression using the
power module substrates after repeating the cooling-heating cycle
(-45.degree. C.125.degree. C.) 4000 times. When cracks were formed
before 3500 cycles, the bonding ratio after 4000 cycles was not
evaluated. Bonding Ratio=(Initial Bonding Area-Peeled Area)/Initial
Bonding Area
In order to determine whether or not there was a nitride layer,
whether or not there is a nitride-forming element at an interface
between the copper plate and the ceramic substrate was determined
based on mapping of the nitride-forming element obtained by EPMA
(electron probe microanalyzer).
In order to obtain the thickness of the Ag--Cu eutectic structure
layer, based on a backscattered electron image of an interface
between the copper plate and the ceramic substrate which was
obtained using an EPMA (electron probe microanalyzer), the area of
the Ag--Cu eutectic structure layer which was continuously formed
on the bonding interface was measured in a visual field (length: 45
.mu.m, width: 60 .mu.m) at a magnification of 2000 times and was
divided by the width of the measurement visual field. The average
of the thicknesses in five visual fields was obtained as the
thickness of the Ag--Cu eutectic structure layer. In the Ag--Cu
eutectic structure layer formed in the bonding portion between the
copper plate and the ceramic substrate, regions which were not
continuously formed on the bonding interface in the thickness
direction were excluded during the measurement of the area of the
Ag--Cu eutectic structure layer.
TABLE-US-00010 TABLE 10 Thickness of Bonding Eutectic Ratio Nitride
Structure Ceramic (After 4000 Layer Layer/.mu.m Cracking Cycles)
Example 1 Present <1 >4000 98.2% According 2 Present 4
>4000 98.7% to 3 Present 8 3500-4000 93.8% Present 4 Present 2
>4000 96.9% Invention 5 Present 5 >4000 99.0% 6 Present 5
>4000 96.9% 7 Present <1 >4000 100.0% 8 Present 2 >4000
97.5% 9 Present 8 3500-4000 98.3% 10 Present <1 >4000 94.8%
11 Present <1 >4000 97.3% 12 Present 2 >4000 94.7% 13
Present <1 >4000 94.8% 14 Present <1 >4000 96.4% 15
Present <1 >4000 96.0% 16 Present 4 >4000 99.7% 17 Present
<1 >4000 94.1% 18 Present <1 >4000 96.3% 19 Present 2
>4000 96.9% 20 Present <1 >4000 95.7% 21 Present 13
>4000 92.8% 22 Present 14 >4000 94.1% 23 Present 14 3500-4000
91.8% 24 Present 15 3500-4000 94.6% 25 Present 14 3500-4000 93.5%
Comparative 1 Present 19 1500-2000 Stopped at Example 2000 Cycles 2
Present 27 0-500 Stopped at 500 Cycles 3 Present 22 500-1000
Stopped at 1000 Cycles 4 None 6 >4000 69.70% Conventional 1
Present 22 1500-2000 Stopped at Example 2000 Cycles
TABLE-US-00011 TABLE 11 Thickness of Number of Bonding Eutectic
Cycles where Ratio Nitride Structure Cracks Were (After 4000 Layer
Layer/.mu.m Formed/Cycles Cycles) Example 51 Present 3 >4000
98.7% According 52 Present 7 3500-4000 97.5% to 53 Present 8
3500-4000 96.3% Present 54 Present 2 >4000 96.7% Invention 55
Present 2 >4000 98.2% 56 Present 9 3500-4000 93.9% 57 Present
<1 >4000 98.5% 58 Present <1 >4000 97.1% 59 Present 4
>4000 95.3% 60 Present 3 >4000 94.0% 61 Present 2 >4000
94.7% 62 Present 2 >4000 96.4% 63 Present <1 >4000 99.0%
64 Present <1 >4000 93.1% 65 Present <1 >4000 96.1% 66
Present 4 >4000 97.3% 67 Present <1 >4000 99.1% 68 Present
<1 3500-4000 95.5% 69 Present 2 >4000 96.5% 70 Present <1
>4000 95.3% 71 Present 15 3500-4000 93.8% 72 Present 14 >4000
94.5% 73 Present 15 3500-4000 91.3% 74 Present 15 3500-4000 92.7%
75 Present 15 >4000 93.4% Comparative 51 Present 23 1500-2000
Stopped at Example 2000 Cycles 52 None 7 3500-4000 64.8% 53 Present
<1 1500-2000 Stopped at 2000 Cycles Conventional 51 Present 22
1500-2000 Stopped at Example 2000 Cycles
TABLE-US-00012 TABLE 12 Thickness of Number of Bonding Eutectic
Cycles where Ratio Nitride Structure Cracks Were (After 4000 Layer
Layer/.mu.m Formed/Cycles Cycles) Example 81 Present <1 >4000
99.5% According 82 Present 6 >4000 99.3% to 83 Present 9
3500-4000 98.1% Present 84 Present 6 >4000 97.4% Invention 85
Present 8 >4000 98.7% 86 Present 7 >4000 99.1% 87 Present 2
>4000 98.6% 88 Present 9 3500-4000 98.4% 89 Present 3 >4000
98.8% 90 Present 8 >4000 98.3% 91 Present 2 >4000 99.1% 92
Present 4 >4000 98.5% 93 Present 14 3500-4000 97.2% 94 Present 3
>4000 95.8% 95 Present 4 >4000 99.4% 96 Present 3 >4000
98.3% 97 Present 3 >4000 98.4% 98 Present 5 >4000 97.4% 99
Present 2 >4000 96.3% 100 Present 3 >4000 99.3%
In Comparative Examples 1 to 3 and 51, the thickness of the
eutectic structure layer was greater than 15 .mu.m, and cracks were
formed on the ceramic substrate at a small number of cycles.
In Conventional Examples 1 and 51, the thickness of the eutectic
structure layer was greater than 15 .mu.m, and cracks were formed
on the ceramic substrate at a small number of cycles similarly to
the case of the comparative examples.
On the other hand, in Examples 1 to 25, 51 to 75, and 81 to 100
according to the present invention in which the thickness of the
eutectic structure layer was 15 .mu.m or less, it was confirmed
that the cracking of the ceramic substrate was suppressed. The
bonding ratio after 4000 cycles was high at 91% or higher.
It was confirmed from the above results that, according to the
examples according to the present invention, a power module
substrate capable of suppressing cracking of a ceramic substrate
during the application of a cooling-heating cycle can be
provided.
In Comparative Examples 3 and 53 in which the content of the
nitride-forming element was 75 mass % or greater, the content of Ag
was small. Therefore, a molten metal region was not sufficiently
formed at the interface between the copper plate and the ceramic
substrate, and cracks were formed before 4000 cycles. In
Comparative Examples 4 and 52 in which the content of the
nitride-forming element was less than 0.4 mass %, a nitride layer
was not sufficiently formed, and the bonding ratio after 4000
cycles was poor at 70% or lower.
On the other hand, in Examples 1 to 25, 51 to 75, and 81 to 100
according to the present invention in which the content of the
nitride-forming element was 0.4 mass % to less than 75 mass %, it
was confirmed that the cracking of the ceramic substrate was
suppressed. The bonding ratio after 4000 cycles was high at 91% or
higher. It was confirmed from the above results that, according to
the examples according to the present invention, even when a copper
member and a ceramic member are bonded to each other, the copper
member-bonding paste capable of suppressing the cracking of the
ceramic member and reliably bonding the copper member and the
ceramic member to each other can be provided.
INDUSTRIAL APPLICABILITY
According to the present invention, in a power module substrate in
which a copper plate formed of copper or a copper alloy is bonded
to a ceramic substrate, the cracking of the ceramic substrate can
be suppressed during the application of a cooling-heating cycle.
Therefore, the present invention has high industrial
applicability.
REFERENCE SIGNS LIST
1 POWER MODULE 3 SEMICONDUCTOR ELEMENT (ELECTRONIC COMPONENT) 10,
110, 210, 310, 410 POWER MODULE SUBSTRATE 11, 111, 211, 311, 411
CERAMIC SUBSTRATE 12, 112, 212, 312, 412 CIRCUIT LAYER 13, 113,
213, 313, 413 METAL LAYER 22, 122, 123, 222, 322, 422 COPPER PLATE
23, 223, 323, 423 ALUMINUM PLATE 31, 131 NITRIDE LAYER Ag--Cu
EUTECTIC STRUCTURE LAYER 41, 441 BUFFER PLATE 50, 250, 350, 450
POWER MODULE SUBSTRATE WITH A HEAT SINK 51, 251, 351, 451 HEAT
SINK
* * * * *